Fiber-optic sources of quantum entanglement

We present a fiber-based source of polarization-entangled photon pairs that is well suited for quantum communication applications in the 1.5 mum band of standard teleco cation fiber. Quantum-correlated signal and idler photon pairs are produced when a nonlinear-fiber Sagnac interferometer is pumped in the anomalous-dispersion region of the fiber. Recently, we have demonstrated nonclassical properties of such photon pairs by using Geiger-mode InGaAs/InP avalanche photodiodes. Polarization entanglement in the photon pairs can be created by pumping the Signac interferometer with two orthogonally-polarized pulses. In this case the parametrically scattered signal-idler photons yield biphoton interference with > 90% visibility in coincidence detection, while no interference is observed in direct detection of either the signal or the idler photons.